Problems with Sieg X2 milling machine

[cplmickey]

For the past day or so my Sieg X2 has been playing up - cutting out as soon as I switched it on and then gradually working for a few seconds at a time until eventually behaving itself as usual. However, today it has refused to work properly and I'm not sure how to investigate the problem. It would seem there are only 2 main parts to it - the motor and the control board, both almost £200 so not a cheap option to try substitution.

What's happening is that the orange overload light comes on almost as soon as I turn the potentiometer to "on" and a relay clicks on the control board, sometimes clicking on and off every couple of seconds. Occasionally the motor spins for a few revolutions before stopping, mostly it doesn't move at all.

I'd assumed it might be a damp problem given the current weather here although my workshop is a wooden shed and doesn't noticably suffer with damp - I use a 100W bar heater on a thermostat to keep the lathe rust free and that is working fine.

I'd be grateful for any advice anyone could give and especially how I might test the motor or control board (the motor is a 230v DC brushed motor so can't just put the mains across it).

Thanks, Ian

[Roger]

It may just be that the brushes have worn right down and the carbon build up is shorting the motor to ground. The extra current may be pulling down the controller.

Before disturbing anything, I'd disconnect the motor and measure from either of the motor wires to ground with a megger. It should be Mega Ohms, but these things can drop down to a few thousands of ohms. This is a common problem I have with the DC Servo motors I service for CNC machines.

I'd then measure the resistance of between the two wires and record that. It will probably be sub 100 ohms.

Then I'd remove the brushes and check their length. If they are really short, they not only need replacing, but at the very least the motor will need blowing our with an air line. You'll get huge plumes of Carbon dust, so you'll have to try to contain that and use a vacuum or take the motor outside.

If you can see the condition of the comutator that's worth checking. It's possible very worn. If it's too bad, you can take the whole thing apart and very carefully turn the comutator with a razor sharp tool after centering it accurately relative to the journals.

If it's a problem with the drive, that's not so easy to check. I've got a lamp load for things like that. You could put as many 100W bulbs in parallel across the output of the drive up to the total wattage of your motor. The lamp brightness will increase as you increase the speed. I do that and then put the oscilloscope across it to see the waveform which shows up nicely because there's no back EMF to mess with the switching.

[cplmickey]

Thanks Roger that's really useful. I'll spend a little time with the motor today and see what I find.

The control board will be more difficult to check although I could try a few bulbs and see what happens. I no longer have access to an oscilloscope though so that's as far as I will be able to go.

[jasonb]

As Roger says check the brushes, make sure you look at both as it's not uncommon for one to wear a lot more than the other.

Board can be tested by replacing motor with a 60 or 100w incandescent light bulb and use the speed control like a dimmer switch.

Failing that have a word with Iain or Brad at ARC next week.

[cplmickey]

Had a word with ARC this morning. They suggest it's most likely the circuit board but they can't test it so I'll use Rogers suggestions for starters. Started to take the motor off but the spindle top nut is locked with a grub screw and I can't find the right allen key to fit - typical isn't it when you've got loads of the things lying around somewhere. Hopefully get that sorted tomorrow.

[cplmickey]

Quick update - the overload protection still kicked in with a lamp in the circuit so looks like it's the board. Everything about the motor seemed ok and it turns freely so hoping the nearly £200 for the control board fixes things. Ian

[runner42]

It's a sign of the times that repair is at the LRU stage i.e board replacement and not at component level. If you are able to check the components on the board that you will usually find that it is the power devices that have failed, these that are the devices connected to the heat sink. It also possible that it has gone short circuit  and using a ohmmeter and look for a zero ohms reading in both directions (reverse ohmmeter leads) i,e a short circuit is causing the failure. Replacement of the faulty device if available could save the cost of a board replacement. This is a big ask for someone without circuit testing skills, but it is something I would try before committing to a board replacement.


Brian 

[Roger]

I'd certainly agree with Brian, power devices are a very common cause of failure, as are Electrolytic capacitors. I'd be looking for short circuits on both of those.
If you're lucky, the power devices will be bolted to the heatsink and have legs soldered through the board. If any of the devices looks to be short circuit, unbolt them and cut the legs off. Then try the circuit again to see if the short has gone.
Never try to desolder these devices intact unless you need to keep them. It's much easier to desolder and pull out the legs when they're cut off. A solder sucker is great for getting the Solder out of a hole, but if you don't have one, an air line could be used once it's hot, but make sure you're wearing safety glasses!

[cplmickey]

Jan 24, 2021 6:46:12 GMT runner42 said:

It's a sign of the times that repair is at the LRU stage i.e board replacement and not at component level. If you are able to check the components on the board that you will usually find that it is the power devices that have failed, these that are the devices connected to the heat sink. It also possible that it has gone short circuit  and using a ohmmeter and look for a zero ohms reading in both directions (reverse ohmmeter leads) i,e a short circuit is causing the failure. Replacement of the faulty device if available could save the cost of a board replacement. This is a big ask for someone without circuit testing skills, but it is something I would try before committing to a board replacement.


Brian 

Hi Brian, yes this is something I considered having started out my career as a microprocessor and electronics repair engineer - although it's been many years I hope I can still remember how to fault find. But I really need my mill up and running so have ordered the board and can then look to repair the old one in my own time. It's a double sided board with surface mount components and these were only just coming in as I left that role so I'm a bit out of my comfort zone. Discreet components on a single sided board were more my thing. Ian

[cplmickey]

Hi Roger. The electolytics look ok I suspect one of the power components - are they FETs? I don't recognise any of the numbers but not surprising after so many years away from the industry. Time for some research.

[Roger]

They probably are FETs of some type if it's a modern device. Just post the numbers here if you can't find the device. Even if it's obsolete, there will be a viable drop in replacement.

[JonL]

Life is so much easier with Google these days to assist finding equivalents.

[Roger]

Jan 24, 2021 20:24:15 GMT JonL said:

Life is so much easier with Google these days to assist finding equivalents.

Isn't it just! I used to have a whole shelf of books which were basically datasheets for things like 74xx and 4xxx logic chips, Microprocessor manuals and Transistor equivalents. When it was initially on line, I used to print them out instead, but I can't remember the time I last printed out a hard copy of anything I use in the workshop. Everything is found in an instant and read off the screen. I'll still download harder to find things so they're readily available for the project I'm working on, but I'm completely paperless these days and I find it much more convenient.

[cplmickey]

The new board came today - it's significantly larger than the old one as you can see here.



Obvious differences are that the MOSFETs have a much larger heatsink and the bridge rectifier is now mounted on a heatsink. Most of the other components are the same although moved around a bit. The connections are a different type but still in the same order.
The new board only just fits into the old box but I need to sort out new mounting points for it - will probably use nylon screws for this. Also bearing in mind the larger heatsinks I'm thinking a few extra ventilation holes won't go amiss.

I've done some fault finding on the old board and not come up with anything yet. The MOSFETs appear ok although the power transistors don't check out as expected but I need to remove them from the board to check properly. Can't find the solder pump although I have some desolder braid so might give that a try.

[Roger]

If you want to preserve the transistors, I'd suggest removing the screw and feeing a piece of wire through the hole so you can pull the device up when it's hot. Then I'd flood the back of the three connections with solder so that I could heat all three of them up to the point where I could pull the transistor out. If you've got more than one soldering iron then another pair of hands would help.
Alternatively, maybe you've got an old fashioned Copper iron that you heat with a blow torch. One of those filed to a sharp point might bridge all three.
You need to get on with it though, you don't want it all hot any longer than you need.

I've made Copper blocks that screw onto the Soldering iron with holes that match the TO220 and larger patterns so I can heat them all at the same time. I still need to flood them with solder, but they come off very easily.

[dscott]

Plenty of HEAT today as my WARCO WM18 motor went up in smoke from getting far too hot???
Yes on a freezing day.

Upon phoning for a replacement was told THAT SOME PEOPLE HAVE FITTED A COMPUTER FAN TO ASSIST WITH KEEPING IT COOL.

Yes it melted the plastic box surrounding it.
Upon looking closer found the tiny slits at the rear USELESS.

Interesting that on your new board that bits like the HEAT SINK have grown.
£260 for a new motor!!!
And they have them in stock???

Well now I have time to get lots of air holes in what is left of the melted plastic box.
A computer fan fitted in the top of it.
Plus on looking at the motor the tiny holes in the base could also have something to do with the heating up.
Yes I had been blaming the bearings for getting hot.
The motor is flange mounted onto the gearbox.
The new version has a brushless motor and is belt drive.
I wonder why.

David, and Lily wondering why I have the windows of the workshop open in January with snow on the ground.

[cplmickey]

Just to finally put this one to bed - it's taken me a while I know.

The new board was a just fit in the existing box but a replacement from ArcEuro seemed to be the same size so decided to use the old box. The old box had lots of stand-offs moulded into it but of course none of them lined up with the holes in the new board so I drilled for M3 nylon screws, nutted them and then fitted M6 nylon nuts over the M3 nuts to act as standoffs. The mains cable entry was in the way so had to be moved and with the larger board the existing earth screws couldn't be used so I made up an earth post and ran an external earth cable to a screw connection on the machine itself. I drilled 7 ventilation holes in the box next to the large heatsink and fitted mesh on the inside to keep out the spiders.

It's all now back together and I have a small mill to use again. I didn't expect it to be quite so involved so I'm hoping it works for a good few years now. Think the existing board worked for about 15 years so fingers crossed for at least the same again.